Process for producing leukocyte-removing material and hydrophilized polyolefins

ABSTRACT

A leukocyte-removing material composed substantially of a polyolefin, the factor of hydrophilicity of the surface of said leukocyte-removing material being less than 40% and not less than 30%.

TECHNICAL FIELD

This invention relates to a leukocyte-removing material composed mainlyof a hydrophobic polyolefin and a process for producing a hydrophilizedpolyolefin material suitable as said leukocyte-removing-material.

BACKGROUND ART

In recent years, various adverse side effects due to contamination withleukocytes have been known in the field of blood transfusion. Forpreventing the side effects, leukocytes are removed by using a materialsuch as highly hydrophilic polyester nonwoven fabric or cotton fabric.In the transfusion of a platelet product, a technique of coating thesurface of a leukocyte-removing material with a hydrophilic polymer orthe like is employed for suppressing the adhesion of platelets to theleukocyte-removing material.

On the other hand, improvements have been made in techniques forselectively removing leukocytes for curing autoimmune diseases such assystemic lupus erythematosus, malignant rheumatoid arthritis, multiplesclerosis, ulcerative colitis and Crohn disease, leukemia, cancer, etc.,or for immunosuppression before transplantation.

Materials such as highly hydrophilic polyester nonwoven fabric, cottonfabric, etc. have been widely used as leukocyte-removing materialsbecause of their high leukocyte-removing capability. From the viewpointof compatibility at the time of contact with blood, an ester structureor an amide structure is generally given to a leukocyte-removingmaterial in order to impart hydrophilicity to the blood contact surfaceof the material. Such leukocyte-removing materials, however, arethermally unstable in the excess of attachment of importance tohydrophilicity. Particularly when the materials are subjected to wetheat sterilization or the like, their hydrolysis or the like is liableto take place. Thus, they are not always satisfactory as materials formedical supplies.

JP-A-3-27317 discloses a leukocyte-removing material obtained bygrafting a monomer onto polyester fiber having a pore major axis of 0.5to 4 μm and a CWST (critical wet surface tension) of 55 to 80 dyne/cm,by means of a radiation. This material, however, is poor in thermalstrength because the polyester fiber or the aforesaid monomer has esterlinkages. Therefore, the grafted monomer is liable to be released bydissolution during wet heat sterilization.

On the other hand, polyolefins are materials having an excellent thermalstability and they can be said to be preferable as materials for medicalsupplies which should be sterilized by high energy, such as wet heatsterilization, because they retain their strength as the materials evenafter the sterilization. The polyolefins, however, have a CWST ofapproximately 25 dyne/cm-30 dyne/cm and hence it has been not suitableto utilize them as they are.

Therefore, JP-A-1-256971 discloses a leukocyte-removing materialcomprising polypropylene nonwoven fabric hydrophilized by plasmatreatment. However, the plasma treatment can impart hydrophilicity tothe material temporarily but the imparted hydrophilicity decreases withthe lapse of time. Thus, the hydrophilicity cannot be stably retainedfor a long period of time. Such a leukocyte-removing material is usedimmediately after the hydrophilization in rare cases and hence should bekept hydrophilized for a certain period or permanently. Accordingly, thehydrophilization by the plasma treatment is not desirable. In addition,when the plasma treatment is carried out, a considerable amount ofelectric charge is produced for increasing the hydrophilicity, so thatthe possibility of complement activation and bradykinin production isincreased. Thus, the material hydrophilized by the plasma treatment isnot desirable as a material for treating blood.

In view of such problems, the present invention is intended to provide aleukocyte-removing material which is hardly decomposed even by wet heatsterilization and has a stable hydrophilicity, and to provide a materialwhich can retain hydrophilicity permanently irrespective of thehydrophobicity of a raw material therefor, has good priming properties,and has an excellent ability to remove leukocytes selectively.

Furthermore, the present invention is intended to provide a process forproducing a hydrophilized polyolefin which retains its hydrophilicityfor a long period of time, without greatly changing characteristics ofpolyolefin.

DISCLOSURE OF THE INVENTION

The present inventors eanestly investigated in order to solve theproblems described above, and consequently found that aleukocyte-removing material comprising a polyolefin and having a factorof hydrophilicity of less than 40% and not less than 30% is veryeffective. Moreover, the present inventors found that theabove-mentioned leukocyte-removing material possesses greatly improvedpriming properties and is surprisingly stable to wet heat sterilization,whereby the present invention has been accomplished.

Thus, one aspect of the present invention is directed to aleukocyte-removing material composed substantially of a polyolefin andhaving a factor of hydrophilicity of less than 40% and not less than30%.

Another aspect of the present invention is directed to a process forproducing a hydrophilized polyolefin which comprises a step ofirradiating substantially a polyolefin with a radiation in a dose ofless than 300 kGy and not less than 15 kGy, and a step of heating saidpolyolefin at a temperature of lower than 125° C. and not lower than 75°C. after the irradiation with the radiation.

The term “leukocyte-removing material” used herein means a material forremoving leukocytes from a leukocyte-containing fluid such as blood or abody fluid by a mechanism such as filtration or adsorption.

BEST MODE FOR CARRYING OUT THE INVENTION

In the leukocyte-removing material of the present invention, the term“composed substantially of a polyolefin” means that theleukocyte-removing material is composed essentially of a modifiedpolyolefin obtained by imparting hydrophilicity to naturally hydrophobicpolyolefin by modification. In detail, the term means that theleukocyte-removing material is composed of a product obtained bychanging (modifying) a polyolefin itself, for example, by irradiationwith a radiation without converting the polyolefin to another material.

Therefore, the leukocyte-removing material “composed substantially of apolyolefin” of the present invention does not include, for example,products obtained by grafting a hydrophilic monomer as another componentonto a polyolefin, and products obtained by coating a polyolefin with ahydrophilic monomer as another component.

The leukocyte-removing material of the present invention may containantioxidants and stabilizers, which are usually contained inpolyolefins. In addition, the leukocyte-removing material of the presentinvention may contain a small amount of a hydrophobic polymer other thanthe polyolefin, for holding of the polyolefin.

The polyolefin refers to a polymer obtained by homopolymerization orcopolymerization of one or more alkenes or alkynes. The polyolefinincludes, for example, polyolefins obtained by homopolymerization, suchas polyethylenes, polypropylenes, polybutylenes, etc., and polyolefinsobtained by copolymerization, such as polypropylene-polyethylenecopolymers, polybutylene-polypropylene copolymers, etc. From theviewpoint of thermal strength, the polypropylenes, polybutylenes,polyethylene-polypropylene copolymers, polyethylene-polybutylenecopolymers, etc. are preferable. From the viewpoint of thecontrollability of the leukocyte-removing material, the polypropylenes,polypropylene-polyethylene copolymers, etc. are the most preferable.

The term “factor of hydrophilicity” used herein is defined as follow:there are prepared aqueous ethanol solutions having predetermined andstepwise varied weight ratios of ethanol to water, a droplet (volume:about 10μL) of each of the solutions is brought into contact with aleukocyte-removing material, starting from the lowest concentration, anda concentration of the aqueous ethanol solution at which saidleukocyte-removing material is wetted for the first time is called thefactor of hydrophilicity. However, depending on the material, thematerial is not completely wetted in some cases because the wetting isdependent on the density of the material. In this case, the factor ofhydrophilicity referred to herein is defined as a concentration of theaqueous ethanol solution at which the contact angle becomes 120° ormore. The term “contact angle” used here means an angle between thedroplet and said leukocyte-removing material. When the contact angle ismeasured on the spherical surface or cylindrical surface of a fiber orthe like, it is defined as an angle made by the droplet outer surfaceand a tangent between the material surface and the center of thedroplet. That is, the contact angle is defined as an angle made by thedroplet and a tangent to the material which touches the material surfaceat the center of the droplet on the portion on which the droplet is incontact with the material. The contact angle can be measured with awell-known contact angle measuring apparatus.

The factor of hydrophilicity of each fibrous material measured by thismethod is 43% for polyethylene nonwoven fabric, 41% for polypropylenenonwoven fabric and 43% for polybutylene fiber. All polyolefin fibershaving a usual composition have a factor of hydrophilicity of more than40%.

The leukocyte-removing material of the present invention should beweakly hydrophilic to such an extent that the factor of hydrophilicityis less than 40% and not less than 30%, from the viewpoint of primingproperties, affinity for blood, and low stimulating properties forblood.

When the factor of hydrophilicity of the material is 40% or more, thematerial has a high hydrophobicity and a low affinity for plasma, sothat it repels blood. Therefore, such a material is not suitable. Inaddition, when the factor of hydrophilicity of the material is 40% ormore, the material cannot be primed with water unless it is pretreatedwith a solution having a relatively high affinity for the material, suchas ethanol. Therefore, troublesome operations are required for priming.Thus, such a material is not suitable.

On the other hand, when the factor of hydrophilicity is less than 30%,the material is increased in hydrophilicity, so that its primingproperties are improved. But, the presence of hydrophilic groupsincreases the possibility of the activation of a large amount ofcomplements and the production of bradykinin during blood treatment.Therefore, such a material is also not suitable.

Polyolefin materials having such a hydrophilicity imparted byirradiation with a radiation that the factor of hydrophilicity is lessthan 30% possess a deteriorated strength and hence are not suitable asmaterials for medical supplies for removing leukocytes.

The factor of hydrophilicity is preferably less than 40% and not lessthan 31%, more preferably less than 39% and not less than 32%.

A porous leukocyte-removing material composed substantially of apolyolefin and having the factor of hydrophilicity according to thepresent invention can be obtained by a method of giving, for example,hydroxyl groups and/or keto groups to a material having a factor ofhydrophilicity of 40% or more, to adjust the factor of hydrophilicity toless than 40% and not less than 30%. Specifically, the factor ofhydrophilicity of the leukocyte-removing material can be adjusted to avalue in a desirable range by giving hydroxyl groups and/or keto groupsby any of {circle around (1)} a method of hydrolyzing ester groups orether groups naturally present in the material, {circle around (2)} amethod of irradiating a polyolefin with a radiation in the presence ofoxygen to form a peroxide surface, and {circle around (3)} a method ofcausing a chemical reaction by the use of an oxidizing agent such assulfuric acid.

Of these, the method of irradiating a polyolefin having no hydroxylgroup with a radiation in the presence of oxygen makes it possible togive hydroxyl groups and/or keto groups so as to attain a desirablefactor of hydrophilicity, most satisfactorily and easily. When theirradiation with a radiation is carried out in air or in the presence ofoxygen, a peroxide is produced in the material. Hydroxyl groups can beintroduced onto the surface by cleaving radicals by pyrolizing thisperoxide in the presence of water or subjecting the peroxide to redoxdecomposition with a reducing agent. Keto groups can also be efficientlyintroduced by the recombination of radicals which takes placesimultaneously. As the radiation, electron beams are most preferablyused from the viewpoint of, in particular, transmittance.

A leukocyte-removing material obtained by irradiating a polyolefin witha radiation in a dose of less than 300 kGy and not less than 15 kGy andheating the polyolefin at a temperature of lower than 125° C. and notlower than 75° C. after the irradiation is preferable from the viewpointof, in particular, stability of hydrophilicity and biocompatibility.

When a slight amount of hydroxyl groups are given to a polyolefin, anyof the well-known methods described above may be adopted, though it itpreferable to give hydroxyl groups and/or keto groups by covalentbinding.

The leukocyte-removing material of the present invention preferably hashydroxyl groups and/or keto groups on the material surface.

The word “surface” used herein means a face which can come in contactwith blood, and it does not include the inside of the material andinternal faces, with which blood cannot come in contact. Therefore,whatever values the factor of hydrophilicity of such portions (theinside of the material and internal surfaces) may have, they need not betaken into consideration in determining the factor of hydrophilicity ofthe surface of the leukocyte-removing material of the present invention.

The leukocyte-removing material of the present invention preferablycomprises, in particular, at least a polypropylene-polypropylenealcohol. The polypropylene-polypropylene alcohol may be either acopolymer of propylene and propylene alcohol, or a material obtained bygiving hydroxyl groups to a polypropylene subsequently by covalentbinding.

In the leukocyte-removing material of the present invention, a porousmaterial having through-holes is effectively used as a raw material.Preferable examples of form of the porous material are a fibrous form,spongy form, foam, etc. Of materials of these forms, fibrous materialsare particularly satisfactorily used as the leukocyte-removing materialfrom the viewpoint of production and the leukocyte-removing capabilityof the final product. Preferable specific examples of form of thefibrous materials are a fibrous form, cotton form, thread form, bundleform, reed screen form, woven fabric form and nonwoven fabric form.Woven fabric and nonwoven fabric are preferable from the viewpoint ofease of controlling the material form, handleability andleukocyte-removing capability.

Nonwoven fabric is the most preferable from the viewpoint of ease ofcontrolling performance characteristics.

The average pore size of the porous material is preferably less than 100μm and not less than 1.0 μm. When the average pore size is less than 1.0μm, the fluidity of blood is undesirably low, namely, the resistance toflow is undesirably increased. On the other hand, when the average poresize is 100 μm or more, the frequency of contact with leukocytes isundesirably decreased because of a decrease in the surface area,resulting in a decreased leukocyte removal rate. In view of the above,the average pore size of the porous material is more preferably lessthan 80 μm and not less than 3 μm, most preferably less than 60 μm andnot less than 5 μm.

The term “average pore size” used herein means the diameter of poresdetermined by a mercury injection method. On the basis of valuesmeasured by the mercury injection method (Poresizer 9320, mfd. byShimadzu Corp.), a graph is drawn by plotting pore volume on the axis ofordinate corresponding to individual pore sizes on the axis of abscissa,and the average pore size is defined as a value corresponding to thepeak of the graph (a mode). As the values measured by the mercuryinjection method, values measured in a pressure range of 1 to 2650 psiaare used.

In the present invention, when the form of the leukocyte-removingmaterial is a nonwoven fabric form, the fiber diameter is preferablythin for increasing the frequency of contact with leukocytes. Theaverage fiber diameter is preferably less than 100 μm and not less than1 μm. From the viewpoint of leukocyte-removing properties, the averagefiber diameter is more preferably less than 50 μm and not less than 1μm, most preferably less than 30 μm and not less than 1 μm.

The average diameter of fibers constituting the nonwoven fabric isdetermined, for example, by taking scanning electron micrographs of thefibers constituting the nonwoven fabric, measuring the diameter of 100or more of the fibers selected at random, and calculating the numberaverage of the measured values.

In the leukocyte-removing material of the present invention, the basisweight of the nonwoven fabric can be measured by a well-known testmethod and is preferably as large as possible from the viewpoint ofstrength. Specifically, the basis weight is preferably 15 g/m² or more.On the other hand, when the basis weight is too large, the flowabilityof blood is deteriorated. Therefore, the upper limit of the basis weightis preferably less than 200 g/m². The basis weight of the nonwovenfabric is more preferably less than 150 g/m² and not less than 20 g/m²,most preferably less than 100 g/m² and not less than 20 g/m².

As the nonwoven fabric used in the present invention, there may be usedeither a single nonwoven fabric or a material obtained by laminating twoor more nonwoven fabrics different in basis weight or average fiberdiameter.

The leukocyte-removing material of the present invention is especiallyexcellent in biocompatibility and can suppress complement activation orbradykinin production. Therefore, the leukocyte-removing material of thepresent invention can be specified by its high biocompatibility.

The concentration of a complement activated by the contact of theleukocyte-removing material with blood is preferably low. Theconcentration of the activated complement is preferably less than 10times and not less than 0.5 time as high as that before the contact. Asan indication of the complement activation, there can be employed theconcentration of an activated complement C3a or C4a, which is easilyformed, and the biocompatibility can be satisfactorily evaluated by thisindication. When the factor of hydrophilicity is less than 30%, a largeamount of hydrophilic groups such as hydroxyl groups are present, sothat the concentration of the activated complement is increased, namely,the biocompatibility is not high. Therefore, such a factor ofhydrophilicity is not very desirable. Accordingly, the concentration ofthe activated complement is more preferably less than 8 times and notless than 0.5 time, most preferably less than 6 times and not less than0.5 time, as high as that before the contact.

The concentration of the activated complement can be measured by amethod such as a well-known radioimmunoassay with two antibodies [NipponRinsho (Japanese Clinic) Vol. 53, Special Number (the last volume)(1995)].

If there is no heating step, a peroxide produced by the irradiation of apolyolefin with a radiation acts as a negative charge, so that thebradykinin concentration is increased, namely, the biocompatibility isnot high. Therefore, the absence of the heating step is not verydesirable.

The concentration of bradykinin produced by the contact of theleukocyte-removing material of the present invention with blood ispreferably low. The bradykinin concentration after the contact ispreferably less than 100 times and not less than 1 time, more preferablyless than 80 times and not less than 1 time, most preferably less than60 times and not less than 1 time, as high as that before the contact.

The bradykinin concentration can easily be measured by a method such asa well-known radioimmuno-assay, enzyme immunoassay or the like.

The leukocyte-removing material of the present invention preferably hasonly a small amount of residual radicals after the irradiation with aradiation from the viewpoint of the stability of the material and thestability of the hydrophilicity. The amount of radicals in thepolyolefin can be measured by means of an electron spin resonance (ESR)apparatus. The amount of residual radicals can be determined also by thefollowing method: at the time of ESR measurement, manganese radicals aremeasured simultaneously with the measurement for the leukocyte-removingmaterial, and there is used a radical intensity ratio obtained bydividing a maximum peak due to radicals remaining in theleukocyte-removing material by a peak due to manganese radicals.

The radical intensity ratio is preferably low because when radicalsremain in the material, they deteriorate the material.

In addition, it was found that when the material is brought into contactwith blood, the bradykinin concentration is increased by the contact ifthe radical intensity ratio is high.

The radical intensity ratio is preferably less than 1/g. When theradical intensity ratio is 1/g or more, the bradykinin concentrationafter the contact is undesirably 100 times or more as high as thatbefore the contact. The radical intensity ratio is more preferably lessthan 0.5/g, most preferably less than 0.1/g.

The hydrophilicity of the leukocyte-removing material of the presentinvention is preferably invariant for a long period of time.Specifically, it is preferably stable for at least 6 months, morepreferably 1 year or more, most preferably 3 years or more, understorage conditions for using the leukocyte-removing material as amedical supply.

The leukocyte-removing material of the present invention can beeffectively used in a leukocyte-removing filter apparatus by packing itinto a container having at least an inlet and an outlet.

When the leukocyte-removing material is used as a packing in theleukocyte-removing filter apparatus, the specification of the packingdensity is important because the state of pores varies depending on thepacking density.

In the leukocyte-removing filter apparatus according to the presentinvention, the packing density is preferably less than 0.40 g/cm³ andnot less than 0.01 g/cm³. When the packing density is less than 0.01g/cm³, the frequency of contact with leukocytes is undesirablydecreased. On the other hand, when the packing density is 0.40 g/cm³ ormore, the pores are undesirably deformed or blocked, resulting innarrowed blood flow paths. In view of the above, the packing density ismore preferably less than 0.35 g/cm³ and not less than 0.01 g/cm³, mostpreferably less than 0.30 g/cm³ and not less than 0.05 g/cm³.

When the leukocyte-removing material is used as a packing in theleukocyte-removing filter apparatus, a spacer material can be laminatedbetween sheets of the leukocyte-removing material. When such a laminatedstructure is used, a pressure change is caused in a blood flow,resulting in aggregation and dispersion of hemocytes, and henceleukocytes can be efficiently removed.

When the leukocyte-removing material and the spacer material arelaminated, they are satisfactorily laminated in a directionperpendicular to a blood flow and/or in a cylindrical form. In thiscase, the specification of the ratio of the leukocyte-removing materialto the spacer material (hereinafter referred to as the lamination ratio)is important. The lamination ratio is calculated by the followingequation.

Lamination ratio=thickness of leukocyte-removing material/thickness ofspacer material

When the lamination ratio is less than 10 and not less than 0.5, anefficient pressure change is caused, so that satisfactory removal ofleukocytes is possible. When the lamination ratio is less than 0.5, theamount of the leukocyte-removing material is relatively decreased, sothat the size of the leukocyte-removing filter apparatus should beincreased. On the other hand, when the lamination ratio is 10 or more,the thickness of the leukocyte-removing material is too large, nosufficient pressure change can be caused in a blood flow. In view of theabove, the lamination ratio is more preferably less than 8 and not lessthan 0.5, most preferably less than 5 and not less than 0.5.

The spacer layer referred to herein is a layer in which blood flows moreeasily than in the leukocyte-removing material layers. As the spacerlayer, there is used, for example, a wide-meshed net of metal orsynthetic resin, inorganic fiber, synthetic fiber, or nonwoven fabrichaving an average fiber diameter larger than that of the nonwoven fabricused as the leukocyte-removing filter layers.

As the spacer material used in the leukocyte-removing filter apparatusaccording to the present invention, a reticular and/or woven-fabric-likematerial or a nonwoven-fabric-like material is satisfactorily used. Themesh size of such a spacer is preferably less than 1,000-mesh and notless than 3-mesh. When the mesh size is 1,000-mesh or more, the spacermaterial undesirably have too fine meshes, so that no sufficientpressure change can be caused in the flow even if the spacer material islaminated with the leukocyte-removing material. On the other hand, whenthe mesh size is less than 3-mesh, the leukocyte-removing materialundesirably enters the meshes of the mesh material, so that nosufficient pressure change can be caused in the flow.

As a method for sterilizing the leukocyte-removing material of thepresent invention, well-known methods such as radiation sterilization,wet heat sterilization, chemical sterilization, etc. are used.

The leukocyte-removing material can be sterilized preferably by wet heatsterilization.

The leukocyte-removing material of the present invention is preferablysterilized in a wet state together with a filling liquid from theviewpoint of its handleability at the time of use and its stabilityduring the sterilization. As the filling liquid, any liquid may besatisfactorily used so long as it does not deteriorate theleukocyte-removing material. The filling liquid is preferably an aqueoussolution which has no undesirable influence on blood and the like evenif the filling liquid remains at the time of use of theleukocyte-removing material. Particularly when leukocytes are removedfrom a blood component, waters such as distilled water for injection,ion-exchanged water, ultrafiltered water, etc., and aqueous solutionscontaining salts are preferably used.

The process for producing a hydrophilized polyolefin of the presentinvention is explained below. By carrying out a step of irradiating apolyolefin with a radiation in a dose of less than 300 kGy and not lessthan 15 kGy, and then a step of heating said material irradiated withthe radiation, at a temperature of lower than 125° C. and not lower than75° C., the polyolefin can be hydrophilized and can be allowed to retainhydrophilicity for a long period of time.

The irradiation of the raw material with a radiation in the presence ofoxygen is preferable because it permits efficient hydrophilization. Forsatisfactory hydrophilization of the polyolefin, the oxygenconcentration is preferably less than 100% and not less than 0.1%, morepreferably less than 50% and not less than 0.1%. Therefore, thepolyolefin can be efficiently hydrophilized by its irradiation in air.

In addition, the specification of the irradiation dose of the radiationis also important in suppressing the deterioration of the raw material.An irradiation dose of the radiation required for hydrophilizing the rawmaterial is less than 300 kGy and not less than 15 kGy. When theirradiation dose of the radiation is less than 15 kGy, no sufficienthydrophilicity is undesirably attainable even if the heating step iscarried out in addition to the irradiation. On the other hand, when theirradiation dose of the radiation is 300 kGy or more, the deteriorationof the raw material is undesirably remarkable. The irradiation dose ofthe radiation is more preferably less than 200 kGy and not less than 15kGy, most preferably less than 100 kGy and not less than 30 kGy.

As the radiation, electron beams, δ-rays, α-rays, β-rays, X-rays, etc.are used. Electron beams or γ-rays are preferably used form theviewpoint of the efficiency of hydrophilization. Electron beams are mostpreferably used from the viewpoint of the suitable transmittance of theradiation.

For the heat treatment after the irradiation, any method may be used solong as it is intended for heating. As a preferable heating method,heating at a dry state, heating in hot water, or heating inhigh-pressure steam is effectively employed. The heating in hot water ismost preferably employed from the viewpoint of ease of operation.

The heating temperature is preferably lower than 125° C. and not lowerthan 75° C. because in this temperature range, the peroxide produced iscleaved and the amount of residual radicals can be rapidly reduced. Whenheating temperature is lower than 75° C., the cleavage of the peroxideis undesirably not sufficient. In this case, when the resulting materialis used as a leukocyte-removing material, the hemocompatibility isdeteriorated by the residual peroxide, so that bradykinin production andthe like are caused. Therefore, such a heating temperature is notdesirable also from the viewpoint of biocompatibility. When the heatingtemperature is 125° C. or higher, the cleavage of the peroxide issufficient but the deterioration of the raw material is undesirablyaccelerated. The heating temperature should be lower than the meltingpoint of the raw material. In view of the above, the heating temperatureis more preferably lower than 125° C. and not lower than 80° C., mostpreferably lower than 121° C. and not lower than 80° C.

In addition, the specification of the heating time is also important.The heating time is preferably less than 200 minutes and not less than 1minute from the viewpoint of the cleavage of the peroxide and thereduction of the amount of residual radicals. When heating time is lessthan 1 minute, the cleavage of the peroxide is undesirably notsufficient. When the heating is conducted for 200 minutes or more, theamount of residual radicals becomes very slight in 200 minutes.Therefore, such heating is not efficient. Thus, the heating time is morepreferably less than 120 minutes and not less than 10 minutes, mostpreferably less than 120 minutes and not less than 15 minutes. When sucha heating time is employed, the cleavage of the peroxide and thereduction of the amount of residual radicals can be efficientlyachieved.

According to the process of the present invention, hydrophilicity can beefficiently imparted to a polyolefin. Since the resulting hydrophilicpolyolefin is not changed in hydrophilicity over a long period of time,is hardly deteriorated as material and contains only a small amount ofresidual radicals and the like, it is suitably used for variouspurposes, in particular, medical purposes and the like.

The present invention is illustrated in further detail with reference tothe following examples.

EXAMPLE 1

Polypropylene nonwoven fabrics (average fiber diameter: 1.7 μm, basisweight: 60 g/m2, polypropylene content 99.99%) were irradiated withelectron beams in five irradiation doses (A: 15 kGy, B: 50 kGy, C: 70kGy, D: 100 kGy, and E: 150 kGy), respectively, in air. Each irradiatednonwoven fabric was poured into hot water at 98° C. to be heat-treatedfor 60 minutes. After the heat treatment, the nonwoven fabric was takenout of the hot water and dried in vacuo at 40° C. for 40 hours to obtaina desired leukocyte-removing material. Table 1 shows the factor ofhydrophilicity of the leukocyte-removing materials after thehydrophilization. A part of each leukocyte-removing material wascompressed and its infrared absorption spectrum was measured with aFourier transform infrared absorption spectrophotometer (FT/IR-7300,mfd. by Nippon Bunko Co., Ltd.) to confirm an absorption due to hydroxylgroup near 3,700 cm⁻¹ and an absorption due to a keto group near 1,700cm⁻¹.

For evaluating the leukocyte-removing capability of eachleukocyte-removing material, five discs with a diameter of 0.68 cm werecut out of each leukocyte-removing material and were packed as filters(packing density 0.1 g/cm3) into a container with a capacity of 1 mlhaving an inlet and an outlet. When priming was conducted by placingdistilled water for injection in the container as a packing liquid, thepriming could be easily achieved. Thus, a desired leukocyte-removingcolumn could be produced.

Into the obtained column was introduced 3 ml of human fresh bloodcontaining ACD-A (blood : ACD-A=8:1 by volume) at a flow rate of 0.5ml/min through the inlet of the column by the use of a syringe pump, andthe treated blood was recovered through the outlet of the column.

The leukocyte removal rate was calculated by counting leukocytes beforeand after the treatment by Turk staining to determine the leukocyteconcentrations before and after the treatment. The leukocyteconcentration before the treatment was 5,200 cells/μL. The leukocyteremoval rate is shown in Table 1.

The leukocyte removal rate (%) was calculated by the following equation:

Leukocyte removal rate=100×(leukocyte concentration beforetreatment−leukocyte concentration after treatment)/leukocyteconcentration before treatment

In this case, platelets were measured with a well-known blood counter.The platelet concentration before the treatment was 400,000 cells/μL.The platelet removal rate is shown in Table 1.

The platelet removal rate (%) was calculated by the following equation:

Platelet removal rate=100×(platelet concentration beforetreatment−platelet concentration after treatment)/platelet concentrationbefore treatment

The pressure before the column was measured with a manometer. Theresults are shown in Table 1.

Further, in this case, the concentration of an activated complement(C3a) (SRL Corp.) and the concentration of bradykinin (SRL Corp.) weremeasured. The C3a concentration was 100 ng/ml before the treatment, andthe bradykinin concentration was 100 pg/ml before the treatment.

The degree of activation for C3a and the degree of bradykinin productionwere calculated by dividing the concentration of each of thesesubstances after the treatment by the concentration thereof before thetreatment. They are shown in Table 1.

In addition, the radical intensity of each nonwoven fabric was measuredwith an electron spin resonance apparatus (JES-FE2XG, mfd. by NipponDenshi Co., Ltd.). In this case, as a control, there were used manganeseradicals (an ESR marker sample manufactured by Nippon Denshi Co., Ltd.was used: the distance between the third and fourth signals among 6 ESRspectra of manganese ion (Mn2+) contained in MnO is constant (86.9Gauss) irrespective of frequency, and the fourth peak is used as areference peak). The radical instensity ratio obtained relative tomanganese is shown in Table 1.

Further, the leukocyte-removing material obtained by employing theirradiation dose D was stored at room temperature in the presence of airfor each of 30 days and 90 days. In both cases, the factor ofhydrophilicity of the leukocyte-removing material after the storage was35%.

Still further, the leukocyte-removing material obtained by employing theirradiation dose D was subjected to an accelerated storage test underthe following conditions. The conditions of the accelerated storage testwere 60° C. for 6 weeks. (Such conditions correspond to storage for 3years; see GUIDELINES FOR INDUSTRIAL RADIATION STERILIZATION OFDISPOSABLE MEDICAL PRODUCTS (IAEA-TECDOC-539) 4.2.1 Materialscompatibility). The factor of hydrophilicity of the leukocyte-removingmaterial after the storage was 35% as before the storage.

In addition, the leukocyte-removing material obtained by employing theirradiation dose D was sterilized in water at 121° C. for 20 minutes byautoclaving. The sterilized leukocyte-removing material was dried at 40°C. for 20 hours. The factor of hydrophilicity of the thus treatedleukocyte-removing material was 35%, namely, the hydrophilicity was notdeteriorated by the sterilization.

COMPARATIVE EXAMPLE 1

The process of Example 1 was repeated except for omitting theirradiation with electron beams. In this case, the factor ofhydrophilicity of the same nonwoven fabric as in Example 1 was 41%. Acolumn packed with the nonwoven fabric was produced in the same manneras in Example 1 and subjected to priming with distilled water forinjection, but the priming could not be conducted because the pressureof the priming liquid on the inlet side was increased. Therefore, thenonwoven fabric was hydrophilized with 1 ml of ethanol and then primedwith 5 ml of distilled water for injection.

In the same blood test as in Example 1, the number of leukocytes wasdecreased to 1,300 cells/μL from 5,200 cells/μL, the number ofleukocytes before the treatment, namely, the leukocyte removal rate was75%. In this case, the number of platelets was decreased to 80,000cells/μL from 400,000 cells/μL, the number of platelets before thetreatment, namely, the platelet removal rate was 80%. Thus, theleukocyte removal rate was decreased by a one-sided flow of leukocyteswhich was attributable to low wettability. During the blood flowing, thepressure before the column of 100 mmHg was increased owing in allprobability to the low wettability. In addition, the activatedcomplement (C3a) concentration ratio and the bradykinin concentrationratio were determined in the same manner as in Example 1 and found to be1.2 and 1.1, respectively.

EXAMPLE 2

A polyethylene foamed sheet (bore diameter 50 μm, thickness 10 mm) wasirradiated with electron beams in an irradiation dose of 100 kGy in airby means of an electron beams irradiation apparatus. The irradiatedfoamed sheet was poured into hot water at 98° C. to be heat-treated for60 minutes. After the heat-treatment, the foamed sheet was taken out ofthe hot water and dried in vacuo at 40° C. for 40 hours to obtain adesired leukocyte-removing material. The factor of hydrophilicity of theleukocyte-removing material after the hydrophilization was 37%. A partof this leukocyte-removing material was compressed and its infraredabsorption spectrum was measured with a Fourier transform infraredabsorption spectrophotometer (FT/IR-7300, mfd. by Nippon Bunko Co.,Ltd.) to confirm an absorption due to hydroxyl group near 3,700 cm⁻¹ andan absorption due to a keto group near 1,700 cm⁻¹.

For evaluating the leukocyte-removing capability of theleukocyte-removing material, two discs with a diameter of 0.68 cm werecut out of the leukocyte-removing material and were packed as filters(packing density 0.05 g/cm³) into a container with a capacity of 1 mlhaving an inlet and an outlet. When priming was conducted by placingdistilled water for injection in the container as a packing liquid, thepriming could easily be achieved. Thus, a desired leukocyte-removingcolumn could be produced.

Into the obtained column was introduced 5 ml of human fresh bloodcontaining ACD-A (blood: ACD-A=8:1 by volume) at a flow rate of 0.5ml/min through the inlet of the column by the use of a syringe pump, andthe treated blood was recovered through the outlet of the column.

The leukocyte removal rate was calculated by counting leukocytes beforeand after the treatment by Turk staining to determine the leukocyteconcentrations before and after the treatment. The leukocyteconcentration before the treatment was 5,200 cells/μL, and that afterthe treatment 800 cells/μL. Thus, the leukocyte removal rate was 84.6%.In this case, platelets were measured with a well-known blood counter tofind that the platelet concentration before the treatment was 400,000cells/μL and that after the treatment 390,000 cells/μL. The plateletremoval rate was calculated in the same manner and found to be 2.5%. Thepressure before the column was 10 mmHg and was not increased. Inaddition, the activated complement (C3a) concentration ratio and thebradykinin concentration ratio were determined in the same manner as inExample 1 and found to be 2.1 and 3.1, respectively.

COMPARATIVE EXAMPLE 2

The same evaluation as in Example 2 was carried out except for omittingthe irradiation with electron beams. In this case, the factor ofhydrophilicity of the same foamed sheet as in Example 2 was 43%.Consequently, blood hardly flowed because of the insufficienthydrophilicity and blood flowing was difficult because of a pressureincrease.

EXAMPLE 3

The process of Example 1 was repeated except for changing theirradiation dose of electron beams to 70 kGy, to obtain aleukocyte-removing material of the present invention. The factor ofhydrophilicity of this leukocyte-removing material was 36%. The nonwovenfabric as the leukocyte-removing material was cut into two 15 cm×70 cmsheets, which were laminated with a sheet obtained by cutting a spacermaterial (a polypropylene mesh (mesh size: 10-mesh)) to the samedimensions as above. The resulting laminate was rolled up into acylinder by the use of a core with a diameter of 1 cm. Thus, thecylinder having a diameter of 4.2 cm and a length of 15 cm (laminationratio: 1) was obtained. In the upper part and lower part of thecylinder, the edges of the laminate were stuck together with apolyurethane adhesive, and a nozzle having a through-hole was attachedto the center of one side of the cylinder. The cylinder was packed intoa container equipped with a nozzle on one side, to produce a desiredleukocyte-removing filter apparatus (packing density: 0.02 g/cm²). Theapparatus was filled with distilled water for injection and sterilizedat 121° C. for 20 minutes by autoclaving. In this case, the inlet ofcolumn was on the nozzle non-attachment side and the outlet of columnwas on the nozzle attachment side.

Into the thus obtained column was introduced 3,000 ml of bovine freshblood containing ACD-A (blood:ACD-A=8:1 by volume) at a flow rate of 50ml/min through the inlet of the column by the use of a roller pump, andthe treated blood was recovered through the outlet of the column.

The leukocyte removal rate was calculated by counting leukocytes beforeand after the treatment by Turk staining to determine the leukocyteconcentrations before and after the treatment. The leukocyteconcentration before the treatment was 5,000 cells/μL, and that afterthe treatment 30 cells/μL. Thus, the leukocyte removal rate was 99.4%.The platelet concentration was 450,000 cells/μL before the treatment and360,000 cells/μL after the treatment, namely, the platelet removal ratewas 20%. The pressure before the column was 25 mmHg and was notincreased.

EXAMPLE 4

The process of Example 1 was repeated except for changing theirradiation dose of electron beams to 100 kGy, to obtain aleukocyte-removing material of the present invention. Thisleukocyte-removing material had a factor of hydrophilicity of 35% and aCWST value of 39 dyne/cm. The leukocyte-removing material was cut into asheet 12.5 cm square. This sheet of nonwoven fabric and the same spacermaterial as in Example 3 were laminated in a lamination ratio of 2 so asto be packed into a container having an inlet and an outlet, whereby adesired leukocyte-removing filter apparatus (packing density: 0.25g/cm²) was obtained.

Into the thus obtained column was introduced 1,000 ml of bovine freshblood containing ACD-A (blood:ACD-A=8:1 by volume) at a flow rate of 25ml/min through the inlet of the column by the use of a roller pump, andthe treated blood was recovered through the outlet of the column.

The leukocyte removal rate was calculated by counting leukocytes beforeand after the treatment by Turk staining to determine the leukocyteconcentrations before and after the treatment. The leukocyteconcentration before the treatment was 5,700 cells/μL, and that afterthe treatment 41 cells/μL. Thus, the leukocyte removal rate was 99.2%.In this case, the platelet concentration was 350,000 cells/μL before thetreatment and 280,000 cells/μL after the treatment, namely, the plateletremoval rate was 20%. The pressure before the column was 25 mmHg and wasnot increased.

EXAMPLE 5

A polypropylene nonwoven fabric (average fiber diameter: 2.9 μm, basisweight: 90 g/m², polypropylene content 99.99%) was irradiated withelectron beams in an irradiation dose of 70 kGy in air. The factor ofhydrophilicity of the irradiated nonwoven fabric was 36%. The irradiatednonwoven fabric was stored under the same conditions as in Example 1 tofind that after 30 days of storage, 90 days of storage and acceleratedstorage, the factor of hydrophilicity of the irradiated nonwoven fabricwas 35%, 34% and 29%, respectively.

COMPARATIVE EXAMPLE 3

A polypropylene nonwoven fabric (average fiber diameter: 1.7 μm, basisweight: 60 g/m², polypropylene content 99.99%) was irradiated withelectron beams in an irradiation dose of 500 kGy in air. The irradiatednonwoven fabric was exposed to hot air at 98° C. to be heat-treated for60 minutes. The factor of hydrophilicity of the leukocyte-removingmaterial after the hydrophilization was 28%. The leukocyte removal rate,platelet recovery, column pressure loss, activated complement (C3a)concentration ratio, and bradykinin concentration ratio were determinedby the same methods as in Example 1 and found to be 99.6%, 20%, 25 mmHg,20 and 150, respectively. Thus, it was found that the biocompatibilityhad been deteriorated. In addition, it was found that by the excessiveirradiation, the tensile strength at break had been decreased to aquarter of that before the irradiation.

COMPARATIVE EXAMPLE 4

A polypropylene nonwoven fabric (average fiber diameter: 1.7 μm, basisweight: 60 g/m², polypropylene content 99.99%) was irradiated withplasma for 120 seconds in a hydrogen stream by means of a plasmairradiation apparatus. After the irradiation, the factor ofhydrophilicity of the nonwoven fabric was 0%. Then, the irradiatednonwoven fabric was stored at 60° C. for 6 weeks in the same manner asin Example 1 to find that its factor of hydrophilicity was decreased to41%. Thus, no lasting hydrophilicity could be imparted.

COMPARATIVE EXAMPLE 5

A polypropylene nonwoven fabric (average fiber diameter: 1.7 μm, basisweight: 60 g/m², polypropylene content 99.99%) was immersed in a 20 w/w% ethanolic solution of an ethylene-vinyl alcohol copolymer (vinylalcohol content 20%) for 10 minutes to be coated with the solution. Thenonwoven fabric was taken out of the solution and dried at 50 for 10hours to obtain coated nonwoven fabric. When this nonwoven fabric wassterilized in water (water: the nonwoven fabric=100:1 by weight) at 121°C. for 20 minutes by autoclaving, appearance of white turbidity wascaused by the peeling-off of the ethylene-vinyl alcohol copolymercoating.

TABLE 1 Factor of Leukocyte Platelet Pressure C3a Bradykinin Radicalhydro- removal removal loss concentra- concentra- intensity Primingphilicity rate (%) rate (%) (mmHg) tion ratio tion ratio ratioproperties A 39 90.2 25 35 1.5 1.2 0.01 Good B 37 99.0 20 25 1.6 1.40.01 Good C 36 99.5 15 18 2.0 1.5 0.01 Good D 35 99.6 10 15 2.1 1.5 0.01Good E 33 99.6 15 12 3.5 5.1 0.01 Good

INDUSTRIAL APPLICABILITY

Since the leukocyte-removing material of the present invention iscomposed substantially of a polyolefin, it is so excellent in thermalstability that its structure is not changed even by wet heatsterilization. Moreover, since said leukocyte-removing material is asuitably hydrophilized material, it is excellent in wettability, caneasily be primed, and has a high leukocyte-removing capability. Thehydrophilicity of said leukocyte-removing material is not deterioratedover a long period of time, and hence the leukocyte-removing materialsufficiently retains its excellent hydrophilicity until it is used as amedical supply.

In addition, a suitable hydrophilicity can be imparted to a hydrophobicpolyolefin material by practicing the process for producing ahydrophilized polyolefin of the present invention. Furthermore, thehydrophilicity is retained for a long period of time without beingdeteriorated over a long period of time. Therefore, the polyolefinmaterial produced according to the production process of the presentinvention is suitable as a material for medical supplies such as, inparticular, a leukocyte-removing material which requires wet heatsterilization.

What is claimed is:
 1. A porous leukocyte-removing material composedsubstantially of a polyolefin, the factor of hydrophilicity of thesurface of said leukocyte-removing material being less than 40% and notless than 30%, wherein the average pore size of said porous material isless than 100 μm and not less than 1.0 μm, wherein said porous materialis a structure made of a non-woven fabric, and which has groups selectedfrom the class consisting of hydroxyl groups and keto groups on thesurface, said non-woven fabric weighing at least 15 g/m² but less than200 g/m².
 2. A leukocyte-removing material according to claim 1, whereinsaid factor of hydrophilicity is less than 39% and not less than 32%. 3.A leukocyte-removing material according to claim 1, wherein the averagepore size of said porous material is less than 100 μm and not less than1.0 μm.
 4. A leukocyte-removing material according to claim 1, whereinthe average fiber diameter of said nonwoven fabric is less than 100 μmand not less than 1 μm.
 5. A leukocyte-removing material according toclaim 1, wherein the polyolefin includes at least polypropylenes.
 6. Aleukocyte-removing material according to claim 1, which is excellent inbiocompatibility.
 7. A leukocyte-removing material according to claim 1,which is not changed in hydrophilicity over a long period of time.
 8. Ahydrophilized leukocyte-removing material composed substantially of apolyolefin, characterized by having an excellent biocompatibility andbeing not changed in hydrophilicity over a long period of time.
 9. Aleukocyte-removing material according to claim 8, obtainable by aproduction process comprising a step of irradiating a material composedsubstantially of a polyolefin with a radiation in a dose of less than300 kGy and not less than 15 kGy, and a step of heating said material ata temperature of lower than 125° C. and not lower than 75° C. after theirradiation with the radiation.
 10. A leukocyte-removing materialaccording to claim 1, obtainable by a production process comprising astep of irradiating a material composed substantially of a polyolefinwith a radiation in a dose of less than 300 kGy and not less than 15kGy, and a step of heating said material at a temperature of lower than125° C. and not lower than 75° C. after the irradiation with theradiation.
 11. A process for producing a hydrophilized polyolefin whichcomprises a step of irradiating a polyolefin with a radiation in a doseof less than 300 kGy and not less than 15 kGy, and a step of heatingsaid polyolefin at a temperature of lower than 125° C. and not lowerthan 75° C. after the irradiation with the radiation.
 12. A processaccording to claim 11, wherein said radiation is electron beams.
 13. Aprocess according to claim 11, wherein said heating step is treatmentwith hot water.
 14. A process according to claim 11, wherein thehydrophilized polyolefin is a biocompatible material.
 15. A processaccording to claim 11, wherein at least one of said radiationirradiation step and said heating step performs sterilization.
 16. Amethod for removing leukocytes from a leukocyte-containing fluid whichcomprises bringing the leukocyte-containing fluid into contact with aleukocyte-removing material composed substantially of a polyolefin andhaving a factor of hydrophilicity of the surface of less than 40% andnot less than 30%, produced by the process of claim 11, and recoveringthe fluid filtered through the leukocyte-removing material.
 17. Ahydrophilized polyolefin produced by the method of claim 11 and having afactor of hydrophilicity of the surface of less than 40% and not lessthan 30%.
 18. A hydrophilized polyolefin according to claim 17, whereinsaid factor of hydrophilicity is less than 39% and not less than 32%.19. A hydrophilized polyolefin according to claim 17, which is porousmaterial.
 20. A hydrophilized polyolefin according to claim 19, whereinthe average pore size of said porous material is less than 100 μm andnot less than 1.0 μm.
 21. A hydrophilized polyolefin according to claim19, wherein said porous material is a structure made of fiber.
 22. Ahydrophilized polyolefin according to claim 21, wherein said structuremade of fiber is a non-woven fabric.
 23. A hydrophilized polyolefinaccording to claim 22, wherein the average fiber diameter of saidnon-woven fiber fabric is less than 100 μm and not less than 1 μm.
 24. Ahydrophilized polyolefin according to claim 17, which has groupsselected from the class consisting of hydroxyl groups and keto groups onthe surface.
 25. A hydrophilized polyolefin according to claim 17,wherein the polyolefin includes at least polypropylenes.
 26. Aleukocyte-removing material according to claim 1, wherein concentrationof a complement C3a OR C4a activated by contact of theleukocyte-removing material with blood is less than 10 times and notless than 0.5 times as high as that before the contact.
 27. Aleukocyte-removing material according to claim 1, wherein concentrationof bradykinin produced by contact of the leukocyte-removing materialwith blood is less than 100 times and not less than 1 time as high asthat before the contact.
 28. A leukocyte-removing filter apparatus whichcomprises a container having at least an inlet and an outlet and aleukocyte-removing material comprising a hydrophilized polyolefin ofclaim 17, packed into said container.
 29. The leukcyte-removing filterapparatus of claim 28, wherein a packing density of saidleukocyte-removing material is less than 0.40 g/cm³ and not less than0.01 g/cm³.
 30. The leukocyte-removing filter apparatus of claim 28,wherein a spacer material is laminated between sheets of saidleukocyte-removing material and both said materials are in a cylindricalform.
 31. The leukocyte-removing filter apparatus of claim 30, wherein alamination ratio of said leukocyte-removing filter and said spacermaterial is less than 10 and not less than 0.5.